Q: Which equation best represents the relationship between osmolarity ($$O$$), solute concentration ($$C$$), and volume ($$V) in a $$compartment?

$$O = \frac{\text{moles of solute}}{\text{liters of solution}}$$

Q: Given the following water distribution in the body: 28L in cells, 11L in interstitial fluid, and 3L in plasma, what percentage of total body water is intracellular?

$$\frac{28}{42} \times 100 = 66.7\%$$

Question 1

Which of the following best describes the role of the proximal tubule in water reabsorption?

Accepted Answer

It reabsorbs 70% of filtered water, and this process is not regulated.

Question 2

What is the primary mechanism by which the medullary osmotic gradient is established in the kidney?

Accepted Answer

Countercurrent exchange involving the loop of Henle.

Question 3

Which equation best represents the relationship between osmolarity ($$O$$), solute concentration ($$C$$), and volume ($$V) in a $$compartment?

Accepted Answer

$$O = \frac{	ext{moles of solute}}{	ext{liters of solution}}$$

Question 4

A patient is given a drug that blocks aquaporin channels in the collecting duct. What is the most likely effect on urine osmolarity?

Accepted Answer

Urine osmolarity will decrease, resulting in dilute urine.

Question 5

Which of the following is TRUE regarding the descending limb of the loop of Henle?

Accepted Answer

It is permeable to water but does not transport Na+, Cl-, or K+.

Question 6

If a person loses a significant amount of blood, which hormone is most likely to be secreted to conserve water?

Accepted Answer

Vasopressin (ADH)

Question 7

Which of the following best explains why water reabsorption in the proximal tubule is not regulated?

Accepted Answer

It follows solute reabsorption via osmosis.

Question 8

A patient with a defect in the Na+-K+-2Cl- transporter in the ascending limb of the loop of Henle would most likely have which of the following consequences?

Accepted Answer

Impaired establishment of the medullary osmotic gradient.

Question 9

Which of the following is a direct effect of vasopressin (ADH) on the collecting duct?

Accepted Answer

Insertion of aquaporin water channels into the apical membrane.

Question 10

Given the following water distribution in the body: 28L in cells, 11L in interstitial fluid, and 3L in plasma, what percentage of total body water is intracellular?

Accepted Answer

$$\frac{28}{42} 	imes 100 = 66.7\%$$

Question 11

Which of the following would most likely increase ADH secretion?

Accepted Answer

Increased plasma osmolarity

Question 12

What is the main function of the vasa recta in the kidney?

Accepted Answer

To maintain the medullary osmotic gradient via countercurrent exchange.

Question 13

Which of the following best describes the effect of maximal vasopressin on urine concentration?

Accepted Answer

Urine becomes highly concentrated, approaching 1200 mOsm.

Question 14

Which process is responsible for the movement of water from the collecting duct into the medullary interstitium?

Accepted Answer

Osmosis

Question 15

A patient with diabetes insipidus lacks functional ADH. What would you expect regarding their urine output?

Accepted Answer

Increased urine output and dilute urine.

Question 16

Which of the following is a consequence of decreased glomerular filtration rate (GFR) due to low body fluid volume?

Accepted Answer

Decreased urine production.

Question 17

Which of the following best describes the countercurrent multiplier system in the loop of Henle?

Accepted Answer

It actively creates an osmotic gradient by differential permeability and active transport.

Question 18

Which of the following is NOT a stimulus for ADH secretion?

Accepted Answer

Decreased plasma osmolarity

Question 19

Which of the following best explains why the ascending limb of the loop of Henle is crucial for urine concentration?

Accepted Answer

It actively transports Na+, Cl-, and K+, creating a hyperosmotic medullary interstitium.

Chapter 20 A: Integrative Physiology II: Fluid and Electrolyte Balance

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